There's a good post at the blog View from the Wing discussing this change. Virgin does partner with Singapore Air, which is a great airline. BUT it seems that, like other Singapore airline partners, Virgin does NOT have full access to Singapore awards, especially the long-hauls trans-Pacific.

You can convert Virgin miles to Hilton points at the ration of 1 mile = 2 points. But in the wake of Hilton's recent massive devaluation, that's not nearly as good a deal as it used to be.